Predicting continental-scale vulnerability of stream invertebrates to climate-change driven alterations to flow and thermal regimes

Abstract:

Climate change is poised to alter flow and temperature regimes in river ecosystems—two major drivers of riverine biodiversity. Compared to vertebrates, freshwater invertebrates are generally better at tracking gradual changes in hydroclimate, due to their higher dispersal abilities, shorter life cycles, and capacity to exploit a wide range of environmental conditions. However, even stream invertebrates could be outpaced by climate change if long-term directional trends and extreme events (hydroclimatic anomalies) increasingly interact in the future. Here, we used a combination of large‑scale physical modeling and time-series analysis to explore vulnerability of stream invertebrate communities. First, we combined European-wide species occurrence data from the Global Biodiversity Information Facility (GBIF) and modelled monthly water temperature and discharge from a physically based water temperature model (DynWat) to determine species-specific hydrological and thermal optima and critical limits. Second, we modeled invertebrate abundance time series from six European river networks spanning 25 degrees of latitude. We estimated temporal change in the discharge and thermal preference of invertebrate communities, responses to hydroclimatic anomalies and trends, and consistency of responses within each river network. Finally, we mapped predicted changes in flow and temperature regimes across Europe, using downscaled and bias-corrected CMIP5 projections from the ISI-MIP project for four emissions scenarios. This mapping enabled identification of areas that are particularly vulnerable to the combined effects of hydroclimatic trends and anomalies, and are dominated by sensitive species (i.e. flow and/or temperature-sensitive species). Vulnerability patterns varied across regions, with northern-most areas being most sensitive to increases in temperature, and southern-most regions to decreases in flow. Our results highlight that when ‘hot moments’ – periods of rapid hydroclimatic change punctuated by extreme events – affect ‘hot spots’ of biotic vulnerability, communities may experience dramatic change. Because invertebrates control key ecosystem processes and sustain aquatic–terrestrial food webs, drastic changes in their communities could ripple through ecosystems.